Mud motors with thrust bearing with enhanced torque

ABSTRACT

An apparatus for use in a wellbore is disclosed that in one non-limiting embodiment includes a rotatable member, a thrust bearing coupled to the rotatable member, wherein the thrust bearing includes a bearing stack that further includes a unitary inner race member that includes a number of axially spaced inner races around an outer surface of the unitary inner race member. A set of bearing elements is placed in each inner race, and a separate outer race secures each set of bearing elements in each inner race.

BACKGROUND 1. Field of the Disclosure

The disclosure relates generally to mud motors for use in a drilling assembly for rotating a drill bit for drilling wells or wellbores.

2. Background Art

Wells or wellbores are formed for the production of hydrocarbons (oil and gas) trapped in subsurface formation zones. A drilling assembly (also referred to as a bottom hole assembly or “BHA”) having a drill bit at end thereof is used for drilling wellbores. Certain drilling assemblies, such as those used for drilling deviated wellbores, utilize a drilling motor, commonly referred to as “mud motor”, to rotates the drill bit to form such wellbores. The mud motor includes a rotor that rotates when a fluid, such as a drilling fluid (commonly known as “mud”), is passed under pressure through the mud motor. The rotor is connected to flexible shaft, which in turn is connected to a drive shaft that connects to the drill bit via a box connection. The drive shaft is supported by an axial bearing (commonly referred to as “thrust bearing”). Currently used thrust bearings include a number individual bearing stacks (often more than 10) that are axially abutted or stacked to form the thrust bearing. Each such individual bearing stack includes a set of rollers or balls placed inside two races. The thrust bearing rotates along with the drive shaft. The drilling assembly and thus the mud motor and the thrust bearing operate in very harsh environment, such as pressures over 10,000 psi and temperatures exceeding 200 degrees Fahrenheit. The drilling assembly and, thus, the thrust bearing, experience very high vibrations and whirl and other mechanical stresses during drilling. Because of the split races for each ball set in currently used thrust bearings, the torque transfer capability over the bearing stacks is limited due to slippage (friction contact) between the bearing stacks. Furthermore, slippage between bearing stacks can also cause wear and damage to the thrust bearing and adjacent parts to the thrust bearing.

The disclosure herein provides a mud motor that includes a thrust that addresses some of the above-noted deficiencies of currently used thrust.

SUMMARY

In one aspect, an apparatus for use in a wellbore is disclosed that in one non-limiting embodiment includes: a rotatable member, a thrust bearing coupled to the rotatable member, wherein the thrust bearing includes a bearing stack that includes unitary race member that includes a plurality of axially spaced inner races around an outer surface of the unitary race member, a set of bearing elements placed in each inner race in the plurality of inner races, and a separate outer race that secures each set of bearing elements in each inner race. In one embodiment, each space between adjacent outer races may be supported or enclosed by a support member made of at least two members for enabling assembly and disassembly of the bearing stack. The at least two members can be half shells that are in contact with their respective adjacent outer races.

In another aspect, a method of assembling an apparatus for use in a wellbore is discloses that in one non-limiting embodiment includes: placing a first set of bearing elements in a first inner race made on an outer surface of a unitary race member having at least two inner races around a the outer surface of the unitary race member; enclosing the first inner race with the first set of bearing elements placed therein with a first outer race member; placing a first support member adjacent the first outer race member; placing a second set of bearing elements in a second inner race adjacent to the first inner race; and enclosing the second inner race with a second outer race member

In yet another aspect, a method of drilling a wellbore is disclosed that in one non-limiting embodiment includes: conveying a drilling assembly in the wellbore that includes a mud motor that rotates a drive member configured to rotate a drill bit at an end of the drilling assembly, a thrust bearing coupled to the drive member, wherein the thrust bearing stack that further includes a unitary race member that contains a plurality of axially spaced inner races around an outer surface of the unitary inner race member, a set of bearing elements placed in each inner race in the plurality of inner races, and a separate outer race that secures each set of the bearing elements in each inner race; and drilling the wellbore by rotating the drill bit by the mud motor.

Examples of certain features of an apparatus and methods have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features that will be described hereinafter and which will form the subject of the claims.

DRAWINGS

For a detailed understanding of the apparatus and methods disclosed herein, reference should be made to the accompanying drawings and the detailed description thereof, wherein like elements are generally given same numerals and wherein:

FIG. 1 shows a cross-sectional view of a section of an exemplary mud motor that includes a thrust bearing stack that contains a unitary member having a number of axially placed inner races that house bearing elements, made according to one non-limiting embodiment of the disclosure;

FIG. 2 shows an isometric sectional view of a partially assembled thrust bearing stack, according to one non-limiting embodiment of the disclosure

FIG. 3 shows an isometric view of an ally assembled thrust bearing stack, according to one embodiment of the disclosure;

FIG. 4 shows a sectional view of the thrust bearing stack shown in FIG. 3; and

FIG. 5 shows an assembled thrust bearing stack shown in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a sectional view of portion of a drilling or mud motor 100 that includes an exemplary thrust bearing (also referred to herein as “thrust bearing assembly) 110 having a bearing stack (also referred to as the “thrust bearing stack”) 130 made according to one non-limiting embodiment of the disclosure. The mud motor 100 forms a lower section of a drilling assembly that is connected to a drill pipe 113 to form a drill string. The mud motor 100 includes a housing 111 that houses a rotor 112 inside a stator 114 The rotor 112 connected to a drive shaft 120 (also referred to as the ‘drive sub”). The drive shaft 120 has a box connection 122 at its end for housing a drill bit (not shown). The rotor 112 rotates inside the stator 114 when a fluid, such a drilling fluid (also referred to as the “mud”) 115, is passed under pressure through the mud motor 100. The fluid 115 passes through a passage or bore 124 in the drive shaft 120 and discharges at the bottom of the drill bit. The wellbore is formed or drilled by rotating the drill bit by the mud motor and/or by rotating the drilling assembly, as is known in the art. The drive shaft 120 is supported by the thrust bearing 110 that includes the bearing stack 130. The bearing stack 130 is connected to the outside of the drive shaft 120 inside the housing 111. A stabilizer 140 is shown disposed around the housing 110. In one non-limiting embodiment, the bearing stack 130 includes a unitary race member 134 that has a number of axially spaced inner races or grooves 133 a-333 n disposed around the outer surface 134 a of the unitary race member 134. A set of bearing elements, such as balls, is placed in each inner race. In FIG. 1, ball sets 130 a-130 n are shown placed in respective inner races 132 a-132 n as described in more detail in reference to FIGS. 2-5. Each inner race containing a set of balls is encased or secured by an outer race. In FIG. 1, outer races 136 a-136 n are shown respectively placed over inner races 132 a-132 n. Drilling assemblies and mud motors are well known in the drilling industry and are thus not described herein in more detail. Although the thrust bearing 110 is described herein in the context of a drilling apparatus, such a thrust bearing may be utilized around a rotatable member of any other apparatus to transfer torque from such member to another device or tool in the form shown and described herein or in an obvious variation thereof.

FIG. 2 shows an isometric view of a partially assembled thrust bearing stack 200 with an exposed view of a unitary body or a race member or housing 210, made according to one non-limiting embodiment of the disclosure. In one embodiment, the unitary inner race member 210 is a solid cylindrical member made from a suitable material, such as steel. In one aspect, the unitary inner race member 210 includes a number of grooves or races 212 a, 212 b through 212 n (also referred to herein as “inner races”) formed around the outer surface 215 of the unitary race member 210. In one embodiment, the inner races 212 a-212 n are axially spaced apart, separated by an equal space between the adjacent races. For example, in FIG. 2, space 214 a separates inner races 212 a and 212 b, space 214 b separates inner races 212 b and 212 c and space 214 n−1 separates inner races 212 n−1 and 212 n. Each inner race includes a set of balls (bearing elements) around such inner race. FIG. 2 shows a set of balls 220 a placed in the inner race 212 a. Each inner race with its set of balls therein is enclosed by a corresponding outer race member that has a race along its inner surface to secure the set of ball therein, as described in detail in reference to FIG. 3. In FIG. 2, an outer race 224 a made of two half shells 234 a and 234 b is shown for placement over the inner race 212 a having balls 220 a therein. Each set of balls enclosed between its inner race and outer race forms an individual stack of the thrust bearing stack 200, wherein such individual stacks or members are axially spaced to form the bearing stack 200.

FIG. 3 shows an isometric sectional view of an assembled thrust bearing stack 300 made according to one non-limiting embodiment for use in an apparatus, such as a mud motor 100 shown in FIG. 1. The thrust bearing stack 300 is shown to include a unitary inner race member 210 having a number of axially spaced grooves or inner races 212 a-212 n on the outside 215 of the unitary inner race member 210. Each of the inner races 212 a-212 n contains a set of balls In FIG. 3, a set of balls 220 a is placed inside and around race 212 a, a set of balls 220 b inside and around inner race 212 b and a set of balls 220 n inside and around inner race 212 n. Each of the inner races 212 a-212 n in the unitary inner race member 210 with its corresponding set of balls 220 a-220 n respectively installed therein is enclosed by a separate outer race member that has an inner groove (referred to herein as the outer race) along an inside surface of such outer race member configured to enclose the ball set in its corresponding inner race. In FIG. 3, an outer race member 224 a having an outer race 232 a encloses the balls 220 a in the inner race 212 a, an outer race member 224 b having an outer race 232 b encloses the inner race 212 b having balls 220 b therein and an outer race member 224 n with an outer race 232 n encloses the inner race 212 n with balls 220 n therein. Each of the outer race members 224 a-224 n may be made by radially placing a number of circular sections or segments, such two or more circular segments for ease of placing and enclosing the balls during assembly process of the thrust bearing stack 300. A support member or a spaces is disposed in each space between adjacent outer race members. Referring to FIGS. 2 and 3, a support member 244 a is shown placed around space 214 a between adjacent outer race members 224 a and 224 b a, a support member 244 b placed around space 214 b between outer race members 224 b and 224 c and a support member 244 n−1 between outer race members 2240 n−1 and 224 n. A support member includes at least two members, placed around each space in the unitary inner race member. The at least two members are half shells that are in firm contact with their respective adjacent outer races. The unitary inner race member 210 includes a through passage 250. The thrust bearing stack 300 is disposed around the outside of the drive 120 of the mud motor 110 (FIG. 1) with the unitary inner race member 210 attached to the drive 120 so that when the drive 120 rotates, the unitary inner race member 210 along with the inner races 212 a-212 n rotates.

Referring now to FIGS. 2 and 3, the outer race members 224 a-224 n may be made of two or more pieces for ease of placing or enclosing the balls in the inner races during assembly of the thrust bearing stack 300. The support members 244 a-244 n−1 may also include two or more members for ease of assembling such members on the thrust bearing stack 300. In one embodiment, a support member may be in the form of two half shells, similar to element 234 a and 234 b of outer races in FIG. 2. Alternatively, all or some of the outer races may be formed inside unitary members (such as unitary shells), wherein a separate outer race corresponds to each of the inner races 212 a-212 n. Such an outer shell may be made of two or more members or pieces (such as half shells, quarter shells, etc.), wherein all such shells placed together over the unitary inner race member enclose all the sets of the bearing elements. Such a structure will not need the support members, as spacing between the outer races will fulfill the same function as the individual support members.

FIG. 4 is a partial sectional view 400 of the thrust bearing stack 300 shown in FIG. 3 during the assembly and disassembly of the thrust bearing stack 300. A method to assemble the thrust bearing stack 300 may include: placing a first set of balls 220 a in a first inner race 212 a made on an outer surface 215 of a unitary inner race member 210 having a selected number of inner races 212 a-212 n around its outer surface 215; enclosing or securing the first set of balls 220 a placed in the first inner race 212 a with a first outer race 224 a; placing a first support member 244 a adjacent the first outer race member 224 a; placing a second set of balls 220 b in a second inner race 212 b and enclosing the second inner race 212 b with the second set of balls 220 placed therein with a second outer race 224 b; and placing a second support member 244 b adjacent to the second outer race member 224 b. This process is continued till all the inner races have been filled with their respective ball sets and secured by their respective outer race members along with the support members placed in the spaces between adjacent outer race members. To disassemble the thrust bearing 400, the above process is utilized in reverse. The support members enable the disassembly of the thrust bearing by providing access to the ball sets during the disassembly process.

FIG. 5 shows an isometric view of a fully assembled thrust bearing stack 300 shown in FIG. 3. The thrust bearing 300 is shown to include the unitary inner race member 210 having a through inner bore 250. The outer races 224 a-224 n respectively enclose the ball sets 220 a-220 n in their respective inner races 212 a-212 n (hidden in FIG. 5). Support members 244 a-244 n−1 are shown placed in the spaces 214 a-214 n−1 between adjacent outer races 224 a-224 n. The thrust bearing disclosed herein having a bearing stack made according an embodiment of this disclosure can provide higher torque transfer compared to the currently used thrust bearings and reduce failures during drilling, such as cracking of the drive sub that includes the thrust bearing and break outs on the drive sub outside diameter caused by torsional movement in between the thrust bearing races.

The foregoing disclosure is directed to certain exemplary non-limiting embodiments of a drilling motor with a thrust bearing. Various modifications will be apparent to those skilled in the art. It is intended that all such modifications within the scope of the appended claims be embraced by the foregoing disclosure. The words “comprising” and “comprises” as used in the claims are to be interpreted to mean “including but not limited to”. Also, the abstract is not to be used to limit the scope of the claims. 

The invention claimed is:
 1. A mud motor, comprising: a drive shaft configured to rotate a drill bit; a thrust bearing coupled to the drive shaft, wherein the thrust bearing includes: a unitary inner race member that includes a plurality of axially spaced inner races around an outer surface of the unitary inner race member; and a set of bearing elements placed in each inner race in the plurality of inner races; wherein each inner race is enclosed by a corresponding separate outer race member, the outer race member securing the set of bearing elements in each inner race, wherein each outer race member is made of two outer race pieces, and wherein a space exists between the two outer race pieces and wherein a separate support member is placed in the space.
 2. The mud motor of claim 1, wherein the unitary inner race member is a solid member.
 3. The mud motor of claim 1, wherein each support member includes at least two members, each such member placed around the space between the outer race members.
 4. The mud motor of claim 3, wherein the at least two members are half shells that are in contact with their respective outer race members.
 5. The mud motor of claim 1, wherein the inner unitary member rotates with the rotatable member.
 6. A drill string, comprising: a drilling assembly comprising: a drilling motor; a drive shaft rotated by the drilling motor to rotate a drill bit at an end of the drilling assembly; and a thrust bearing coupled to the drive shaft, the thrust bearing including: a unitary inner race member that includes a plurality of axially spaced inner races around an outer surface of the unitary inner race member; and a set of bearing elements placed in each inner race in the plurality of inner races; wherein each inner race is enclosed by a corresponding separate outer race member, the outer race member securing the set of bearing elements in each inner race, wherein each outer race member is made of two outer race pieces, and wherein a space exists between the two outer race pieces and wherein a separate support member is placed in the space.
 7. The drill string of claim 6, wherein the unitary inner race member is a solid member.
 8. The drill string of claim 7, wherein each support member includes at least two members placed around each space between the outer race members.
 9. The drill string of claim 8, wherein the at least two members are half shells that are in firm contact with their respective adjacent outer race members.
 10. A method of assembling an apparatus for use in a wellbore, the method comprising: providing a unitary inner race member having a plurality of races around an outer surface thereof; placing a first set of balls in a first inner race of the plurality of inner races; enclosing the first inner race with the first set of balls placed therein with a first outer race member to secure the first set of balls in the first inner race, the first outer race member being made of at least two outer race pieces; placing a first support member adjacent to the first outer race member; placing a second set of balls in a second inner race in the plurality of inner races; enclosing the second inner race with the second set of balls placed therein with a second outer race member to secure the second set of balls in the second inner race, the second outer race member being made of at least two outer race pieces, wherein the first support member is adjacent to the second inner race; and placing a second support member adjacent to the second outer race member.
 11. The method of claim 10, wherein the unitary inner race member is a solid member.
 12. The method of claim 10, wherein each of the first and second support members comprises two half shells.
 13. A method of drilling a wellbore, comprising: conveying a drilling assembly in the wellbore that includes: a mud motor that rotates a drive member that in turn rotates a drill bit at an end of the drilling assembly; a thrust bearing coupled to the drive member, wherein the thrust bearing includes a unitary inner race member that contains a plurality of axially spaced inner races around an outer surface of the unitary inner race member, and a set of bearing elements placed in each inner race in the plurality of inner races, wherein each inner race is enclosed by a corresponding separate outer race member, the outer race member securing the set of bearing elements in each inner race, wherein each outer race member is made of two outer race pieces, and wherein a space exists between the two outer race pieces and wherein a separate support member is placed in the space; and drilling the wellbore by rotating the drill bit by the mud motor. 